1. Field of the Invention
The present invention relates generally to a current location indicating device for use in a vehicle. More particularly, the invention relates to an improved apparatus for determining and visually indicating a current location of an automotive vehicle to the driver thereof, wherein a stable and quick-start locating operation is attained from the combination of an earth magnetism sensor and a rate gyroscope.
2. Description of Relevant Art
A known apparatus has been developed for the determination and visual indication of a current location of an automotive vehicle to the driver thereof, which comprises a travel distance counter section adapted to determine the current mileage or travel distance of an automotive vehicle in terms of, for example, the travel speed thereof, and a bearing detector section adapted to detect the current orientation and extent of azimuthal deviation of the vehicle in accordance with the travel direction thereof per a given distance from its starting point. The current location of the vehicle along its travel route is calculated arithmetically from the thus-obtained detection data, the result of which calculation is visually indicated on display for the driver of the vehicle, by way of spot information varying from time to time, upon a suitable road map on the display showing the travel route along which the vehicle is currently travelling.
In the known travel route indication apparatus of the aforesaid type, there is employed a bearing or orientation detecting means such as a rate gyroscope or the like which is adapted to detect a possible angular velocity as produced about the axis of yawing motion of the vehicle when it is turned one way or another while travelling. Although such gyroscope is advantageous in that it normally provides an accurate bearing detection for a relatively short period of service with sufficient insensitivity to external disturbances, it is disadvantageous in that it suffers from a rather poor initial or rise characteristic when powered-up, inasmuch as some time is required before it is ready to serve with a stable performance for a bearing detection.
On the other hand, it is known to provide an earth magnetism sensor serving as a bearing detection means, which is designed to sense the earth magnetism so as to detect a current relative relationship such as, for example, a current angular relationship between the orientation of the horizontal component of the earth magnetism and a current travel direction of the vehicle. Such an earth magnetism sensor can immediately provide a current bearing detection upon the switching-on of the power supply, however, it is inevitable that such particular magnetism sensor will be substantially susceptible to external disturbances from structures such as a railroad crossing and an iron bridge, or a large-sized truck having an iron box or housing passing by and alongside the vehicle in which the bearing detector of such type is provided.
With the conventional arrangement for detecting a current location of an automotive vehicle of the type as described above, it is very possible that spot information showing a current location of the vehicle on the display at the driver's seat will deviate from a predetermined course of travel due to thus-far accumulated errors in the detection as created from possible drifts of the gyroscope while the vehicle is travelling, to such an extent that such information will indicate an erroneous location of the vehicle on the display screen. When the vehicle is under such conditions, it is very difficult or even impossible for the driver of the vehicle to determine whether the displayed information on the screen is incorrect or if the vehicle is actually travelling in a different or incorrect way, resulting in substantial ambiguity.
The present invention effectively overcomes the aforesaid inconveniences and difficulties experienced with the conventional location detecting apparatus for use in an automotive vehicle.